This invention relates to a microbiological testing apparatus and method of use. More particularly, it relates to a device and method for determining the minimum concentration of antibiotics necessary to inhibit the growth of microorganisms, i.e., bacteria. This concentration is sometimes referred to hereinafter as the minimum inhibitory concentration.
The large number of strains of highly pathogenic bacteria and their varying susceptability to antibiotics has resulted in the development of microtitration techniques for determining the minimum inhibitory concentration. These techniques typically involve the use of microtitration plates which comprise, for example, a one-piece, plastic shell containing a plurality of recepticals or incubation wells. The wells may be arranged in parallel rows such as is described in U.S. Pat. No. 3,356,462, or in a circular pattern such as is described in U.S. Pat. No., 3,441,383. In any event, during the test, the wells contain the microorganism to be inhibited, nutrient broth and antibiotic. Typically each of the wells contains a different concentration of antibiotic. The contents of the wells are incubated for a period of time and are then studied so as to determine the minimum inhibitory concentration of the antibiotic.
In the past the determination of minimum inhibitory concentration has been made by illuminating the incubated wells and then viewing the contents either directly from above or indirectly by observing a reflected image of the contents. Those wells which contain a sufficient concentration of antibiotic to inhibit the growth of the microorganisms contain a clear solution, while those wells which contain an insufficient concentration of antibiotic have either a turbid solution or a small turbid area or dot surrounded by clear solution therein.
It is frequently difficult to determine when the contents of the incubated wells comprise a clear solution. This is especially true when the contents are either lightly turbid or a small turbid dot surrounded by clear solution. Accordingly, it would be highly desirable to provide a device and process which enhances the visibility of the contents of the incubation wells and simplifies the ability to determine the minimum inhibitory concentration.